1. Field of the Invention
The present invention relates to the manufacturing of semiconductor light-emitting devices using indium gallium nitride (InGaN) semiconductor material. More specifically, the present invention relates to a technique for epitaxially growing high-quality semiconductor material with a multi-quantum well (MQW) structure.
2. Related Art
Group III-V nitride compounds (e.g., GaN, InN, and AIN) and alloy-compounds (e.g., AlGaN, InGaN, and AlGAlnN) have demonstrated efficient luminescence in the blue-green spectrum. This efficiency has been the driving force for their recent application in light-emitting diodes (LEDs) and laser diodes, which in turn has changed the market for color displays. Using group III-V nitride materials for high-brightness LEDs has opened the door to many applications previously deemed unfeasible, such as in traffic lights and in flat-panel display as white light sources. In addition, ultra-violet laser diodes using group III-V nitride materials are now widely used in scientific instrumentation, laboratories, and commercial products.
The active region of an LED is the area where light is generated. It typically includes a multi-quantum well (MQW) structure, which includes multiple periods of quantum well structures. A single quantum well structure may include, for example, an indium gallium nitride (InGaN)-based potential well (well) sandwiched between potential barriers (barriers) based on gallium nitride (GaN) or aluminum gallium nitride (AlGaN) materials. Carriers are trapped in the well between the barriers. An MQW structure allows higher carrier density and hence increases the carrier recombination rate. The faster the carriers recombine, the more efficient a light-emitting device becomes.
One of the factors that determine the color of the light emitted by an LED is the concentration of indium (In) in the MQW structure. Specifically, the color of the light emitted by an LED can vary with different InGaN concentration or InGaN-to-GaN ratios in the MQW structure. The higher the concentration of In or InGaN-to-GaN ratio, the longer the wavelength of the visible light. For instance, an LED emitting green light may exhibit a higher concentration of In in the MQW structure than one emitting blue light because the wavelength of green light is longer than that of blue light. One of the challenges of producing light with longer wavelengths is to increase the concentration of In in the MQW structure while maintaining the quality of the MQW structure.
Typically, the LED-fabrication process involves subjecting the structure to a relatively high temperature to obtain a high-quality MQW structure. In a conventional method, the InGaN well in an MQW structure is grown at a moderate temperature to increase the concentration of In, and the temperature is subsequently raised at least 100° C. for the growth of GaN barriers.
The temperature for fabricating an MQW structure is ideally lower than 800° C. to avoid the breaking of the indium-nitrogen bond in the InGaN well. However, fabricating an MQW structure at a lower temperature could result in a low-quality MQW structure.